The major goal of this project is to better understand the response of individual mammalian cells to extracellular signals. We have previously described modulation of hormone/neurotransmitter receptors on cultured human cells by manipulation of medium components and induction of receptor synthesis and expression by short-chain fatty acids (e.g. butyrate). During this reporting period we have continued to emphasize the growth of human cells in serum-fre, chemically-defined media; this approach permits experimentation which is not feasible in the presence of serum. For example, our finding of a role for epidermal growth factor in the maintenance of beta-adrenergic receptor expression could only have occurred in serum-free media. We have recently found a strong synergistic effect on beta-adrenergic receptor induction between butyrate and the nucleoside analogue 5-azacytidine which has been reported to induce differentiation by a mechanism involving DNA hypomethylation. However, we have also found comparable synergism with a variety of similar analogues including many which do not cause DNA hypomethylation; these findings should permit further understanding of regulation of receptor synthesis and the mechanism(s) of induction by fatty acids and nucleoside analogues. We have also found a transport site for catecholamines with a unique and previously undescribed specificity, distinct from both alpha- and beta-adrenergic receptors, on cultured human cells; transport at this site is dependent on an electrochemical proton gradient across the plasma membrane.